U.S. patent number 5,159,404 [Application Number 07/801,451] was granted by the patent office on 1992-10-27 for diode-array spectrometer.
This patent grant is currently assigned to Carl-Zeiss-Stiftung. Invention is credited to Reinhold Bittner.
United States Patent |
5,159,404 |
Bittner |
October 27, 1992 |
Diode-array spectrometer
Abstract
A transparent carrier body of a diode-array spectrometer having
a concave grating is configured as a biconvex lens and the diode
array is mounted at a distance (d) to a second convex surface lying
opposite the concave grating. Preferably, the radii of curvature
(r.sub.1, r.sub.2) differ from each other only slightly. A
simplified manufacture and adjustment is possible with good optical
correction.
Inventors: |
Bittner; Reinhold (Schwabisch
Gmund, DE) |
Assignee: |
Carl-Zeiss-Stiftung
(Heidenheim, DE)
|
Family
ID: |
6419558 |
Appl.
No.: |
07/801,451 |
Filed: |
December 2, 1991 |
Foreign Application Priority Data
Current U.S.
Class: |
356/328 |
Current CPC
Class: |
G01J
3/0259 (20130101); G01J 3/20 (20130101); G01J
3/2803 (20130101) |
Current International
Class: |
G01J
3/20 (20060101); G01J 3/12 (20060101); G01J
3/28 (20060101); G01J 003/18 (); G01J 003/36 () |
Field of
Search: |
;356/326,328
;385/37 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Planar Rowland Spectrometer for Fiber-Optic Wavelength
Demultiplexing" by H. W. Yen, Optics Letter, vol. 6, No. 12, Dec.
1981, pp. 639 to 641..
|
Primary Examiner: Evans; F. L.
Attorney, Agent or Firm: Ottesen; Walter
Claims
What is claimed is:
1. A diode-array spectrometer comprising:
a transparent carrier body defining a biconvex lens having first
and second convex surfaces;
a concave grating mounted on said first convex surface;
a diode array lying opposite said second convex surface; and,
mounting means for holding said diode array so as to cause said
second convex surface and said diode array to conjointly define a
small spacing (d) therebetween.
2. The diode-array spectrometer of claim 1, further comprising
optical means mounted on said second convex surface for defining an
entrance slit through which light to be spectrally analyzed passes
into said biconvex lens.
3. The diode-array spectrometer of claim 1, said first and second
convex surfaces having respective radii of curvature (r.sub.1,
r.sub.2) and said radii of curvature (r.sub.1, r.sub.2) differing
only slightly.
4. The diode-array spectrometer of claim 3, said first and second
convex surfaces defining first and second apeces and said first
radius of curvature r.sub.1 having a center of curvature lying in
the immediate proximity of said second apex and said second radius
of curvature having a center of curvature in the immediate
proximity of said first apex.
5. The diode-array spectrometer of claim 1, said concave grating
being holographically corrected.
6. The diode-array spectrometer of claim 1, said carrier body being
spherical.
7. The diode-array spectrometer of claim 1, said carrier body being
cylindrical.
Description
FIELD OF THE INVENTION
The invention relates to a diode-array spectrometer having a
concave grating and a transparent carrier.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,707,056 discloses spectrometers and demultiplexers
having mechanically divided or holographic concave gratings. The
entrance slit and exit plane lie substantially on the Rowland
circle. In a compact and robust embodiment, the optical components
are mounted on a glass or plastic body. It is known to arrange a
diode array in the exit plane in spectrometers of this kind.
However, a considerable danger of breakage exists with the required
cementing of the diode array to the spectrometer. Furthermore,
commercially available diode arrays are built into housings and for
this reason cannot be mounted directly on the spectrometer
body.
A planar Rowland spectrometer is disclosed in the paper of H. W.
Yen et al entitled "Planar Rowland Spectrometer for Fiber-Optic
Wavelength Demultiplexing" published in the journal "Optics
Letters", Vol. 6, no. 12, December 1981, pages 639 to 641. This
planar Rowland spectrometer has a base body in the form of a slab
waveguide on which a cylindrical concave grating is mounted. The
slab waveguide has an end face facing away from the grating which
has the contour of the Rowland circle. Radially arranged
light-conducting fibers operate as signal outputs.
SUMMARY OF THE INVENTION
It is an object of the invention to configure a diode-array
spectrometer of the kind referred to above so that it is suitable
for utilizing diode arrays which are mass produced. It is another
object of the invention to configure such a diode-array
spectrometer so that it is simple to assemble and adjust and so
that the imaging errors, especially the coma, can be well
corrected.
The above objects are achieved with a diode-array spectrometer
having a concave grating and a transparent carrier.
The invention proceeds from the premise that a reliable assembly of
mass produced diode arrays requires an air gap relative to the
transparent carrier. In this way, the possibility for correcting
tolerance variations of the carrier body is provided by displacing
and tilting the diode array for adjustment.
However, the boundary surface of the carrier body to air is now an
additional refracting surface because of which imaging errors and
especially coma arise. The invention permits the utilization of the
advantages of the air gap without the disadvantages thereof by
introducing an arcuate optical surface in lieu of a planar optical
surface. For manufacture, this presents no problem and in
principle, a cylindrical form is adequate when the divergence of
the illuminating beam entering through the entrance slit is not too
great. If a lightwave guide of the kind is utilized as in the
arrangement described in the article of H. W. Yen et al, then this
likewise applies. A spherical form is easily suited and simpler
from a manufacturing view point than a cylindrical form.
In Yen et al, the carrier follows the Rowland circle on the end
face thereof facing away from the grating with the radius of the
Rowland circle being half the radius of the grating and with the
curvature center of the circle being at the center of the lens. In
contrast to the planar Rowland spectrometer of Yen et al, both
radii of curvature in the diode-array spectrometer of the invention
differ only slightly from each other and each curvature center lies
near the curvature apex of the other convex surface.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now be described with reference to the single
FIGURE of the drawing showing the diode-array spectrometer of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The diode-array spectrometer of the invention includes a
transparent carrier 2 made, for example, of glass produced under
the designation UBK 7 which is commercially available from Schott
Glaswerke of Germany. A concave grating 1 is mounted on the first
convex surface 21 of the carrier body 2. A small air gap (d) of for
example 1.8 mm is provided between the second convex surface 22 and
a diode array 3 disposed in a housing 31. In the adjusted position,
the diode array 3 is fixed by means of an epoxy adhesive 32 or the
like to the carrier body 2.
In the embodiment shown, the carrier body 2 is a spherical lens
having a center thickness of 28.26 mm, with the radius r.sub.1 of
the first convex surface 21 and of the grating 1 being 29.64 mm and
with the radius r.sub.2 of the second convex surface 22 being 28.18
mm. Thus, the radius r.sub.2 of the second convex surface 22
differs only slightly from the radius r.sub.1.
An entrance slit 4 having for example a width of 50 .mu.m and a
height of 2,500 .mu.m is arranged on the second convex surface 22
next to the diode array.
The light to be analyzed spectrally can be supplied to the entrance
slit 4 in any desired manner such as via a light-conducting fiber
(not shown).
The electronics and the software for operating the diode array 3
and the signal evaluation is likewise not shown and is well known
for desired applications of photodiode arrays.
With a grating of 366 lines per millimeter, the spectrometer of the
embodiment has a dispersion which has good linearity for
wavelengths of 360 to 780 nm with the dispersion being 132 nm/mm
and with individual photodiodes having a width of 25 .mu.m in the
diode array 3, a resolution better than 10 nm is obtained.
The precise determination of the lens geometry of the carrier body
2, the position and magnitude of the entrance slit 4 and the
position of the diode array 3 for minimizing all imaging errors and
for optimally linearizing the spectrum, is obtained in the context
of the invention utilizing known means of optic computation.
In lieu of a grating 1 defined primarily by the mechanical ruling
of the grating, a further improvement is obtained by utilizing a
grating with additional error correction by means of holographic
manufacture.
In lieu of air, another medium can be provided in the gap between
the carrier body 2 and the diode array 3.
It is understood that the foregoing description is that of the
preferred embodiments of the invention and that various changes and
modifications may be made thereto without departing from the spirit
and scope of the invention as defined in the appended claims.
* * * * *